Babyish learner treated thus? (8)

I believe the answer is:

shabbily

'thus?' is the definition.
Both the answer and definition are adverbs. Perhaps there's a link between them I don't understand?

'babyish learner treated' is the wordplay.
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'treated' is an anagram indicator.
'babyish'+'l'='babyishl'
'babyishl' is an anagram of 'SHABBILY'.

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app